BG Sulfa Agar

Intended Use

BG Sulfa Agar is used for isolating Salmonella.

Summary and Explanation

Salmonellosis continues to be an important public health problem worldwide, despite efforts to control the prevalence of Salmonella in domesticated animals. Infection with non-typhi Salmonella often causes mild, self-limiting illness. The illness results from consumption of raw, undercooked or improperly processed foods contaminated with Salmonella. Many of these cases of Salmonella-related gastroenteritis are due to improper handling of poultry products. Various poultry products are routinely monitored for Salmonella before their distribution for human consumption, but in many instances, contaminated food samples elude detection. BG (Brilliant Green) Sulfa Agar is a highly selective medium. Osborne and Stokes¹ added 0.1% sodium sulfapyridine to Brilliant Green Agar to enhance the selective properties of this medium for Salmonella. This formula is recommended as a selective isolation medium for Salmonella following enrichment. ² It is also recommended for direct inoculation with primary specimens for Salmonella isolation.
For food testing, BG Sulfa Agar has been used for detection of Salmonella in low and high moisture foods.^3-4 It has also been used for detecting Salmonella in feeds and feed ingredients.⁵ This medium is recommended when testing foods for Salmonella following USDA guidelines.^6-8

Principles of the Procedure

In BG Sulfa Agar, peptone and yeast extract provide nitrogen, vitamins and minerals. Lactose and sucrose are the sources of carbohydrates in the medium. Brilliant green and sodium pyridine are complementary in inhibiting gram-positive bacteria and most gram-negative bacilli other than Salmonella spp. Phenol red is the pH indicator that turns the medium a yellow color with the formation of acid when lactose and/or sucrose is fermented. Agar is the solidifying agent.

User Quality Control

Identity Specifications
BG Sulfa Agar
Dehydrated Appearance: Pink, free flowing, homogeneous.
Solution:                       5.9% solution, soluble in purified water upon
                                    boiling. Solution is very dark amber, very slightly
                                    to slightly opalescent.
Prepared Appearance:     Orange-brown to dark reddish-amber, slightly
                                    opalescent.
Reaction of 5.9%
Solution at 25°C:            pH 6.9 ± 0.2
Cultural Response
BG Sulfa Agar
Prepare the medium per label directions. Inoculate and incubate at 35 ± 2°C for 18-48 hours.

Formula

BG Sulfa Agar
Approximate Formula* Per Liter
Yeast Extract................................................................ 3.0 g
Proteose Peptone No. 3............................................... 10.0 g
Lactose...................................................................... 10.0 g
Saccharose................................................................. 10.0 g
Sodium Sulfapyridine..................................................... 1.0 g
Sodium Chloride........................................................... 5.0 g
Agar.......................................................................... 20.0 g
Brilliant Green.......................................................... 12.5 mg
Phenol Red................................................................ 0.08 g
*Adjusted and/or supplemented as required to meet performance criteria.

Directions for Preparation from Dehydrated Product

1. Suspend 59 g of the powder in 1 L of purified water. Mix thoroughly.
2. Heat with frequent agitation and boil for 1 minute to completely dissolve the powder.
3. Autoclave at 121°C for 15 minutes. Avoid overheating, which will decrease selectivity.
4. Test samples of the finished product for performance using stable, typical control cultures.

Procedure

Refer to appropriate references for specific procedures for the isolation and cultivation of Salmonella from meat, poultry and egg products and other foods.^2,7,8

Expected Results

The typical Salmonella colonies appear as pink-white to red opaque colonies surrounded by a brilliant red medium. The few lactose and/or sucrose fermenting organisms that grow are readily differentiated due to the formation of a yellowgreen colony surrounded by an intense yellow-green zone. BG Sulfa Agar is not suitable for the isolation of S. Typhi or Shigella; however, some strains of S. Typhi may grow forming red colonies.

Limitations of the Procedure

1. On BG Sulfa Agar colonies of Salmonella spp. vary from red to pink to white depending on length of incubation and strain.¹³
2. BG Sulfa Agar is normally orange-brown in color; however, on incubation, it turns bright red and returns to normal color at room temperature.¹³
3. S. Typhi does not grow adequately on BG Sulfa Agar. Shigella spp. do not grow on BG Sulfa Agar.¹³
4. Do not autoclave BG Sulfa Agar longer than 15 minutes; longer periods decrease the selectivity of the medium.
5. Since BG Sulfa Agar is highly selective, it is recommended that less selective media, such as MacConkey Agar, be used simultaneously.

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